Peel or scrape ginger with a paring knife. Using a mandolin, slice ginger as thinly as possible (no thicker than 1/16th inch).
Fill a medium size saucepan half full with water. Bring it to a boil. Scald ginger for 20 to 30 seconds. Remove with a metal strainer into sterilized jars.
Combine rice vinegar, sugar, and kosher salt in a small saucepan over medium heat. Stir until sugar and salt dissolve. Let it come to a boil, and then turn off heat.
Pour vinegar mixture into the jar to completely cover the ginger. Place the lid on and allow it to cool completely before transferring to the refrigerator.
Pickled ginger may be eaten in 2 to 3 days. Keep refrigerated for 2 to 3 months.